The goal of this proposal is to establish a molecular basis for the interaction of nuclear receptors with the JUN/FOS proto-oncogene complex AP-1. In previous studies, we have reported that AP-1 is able to block hormonal induction by the retinoic acid receptor. Recently, we have shown that AP1 is also able to block induction by the glucocorticoid receptor. Similarly, we have evidence that this inhibition may be reciprocal such that retinoic acid or glucocorticoids may be able to inhibit induction of promoters containing AP-1 sites. This proposal is directed towards understanding the interaction of these two regulatory circuits in greater detail. Specifically, we will utilize co-transfection studies to characterize the cross-regulation of the RAR and the GR with the AP-1 network and reciprocally, of AP-1 with the nuclear receptor network. Utilizing site-directed mutations and deletion mutants, we will identify the regions in JUN and FOS that are necessary for inhibition of nuclear receptor activity. Reciprocally, we will identify regions in the RAR and GR that mediate inhibition of AP-1 action. We will characterize the molecular interactions of the RAR and the GR with AP-1 by defining the potential formation of a heterodimeric or heterotrimeric complex. These complexes will be characterized through amino precipitation studies and DNA mobility shift analysis. Antibodies will be used to characterize potential formation of heterodimers or heterotrimers and ultimately, the molecular structure of a putative interaction interface will be characterized. These domains will be chemically synthesized, purified, and associated and their structure characterized by 2-D NMR as well as X-ray absorption analysis.